1. Field of the Invention
The invention relates to measurement of movement using Fiber Bragg Grating.
2. Description of the Background Art
During normal loading, ligaments generally experience strains of one to two orders of magnitude larger than relatively stiff tissues, such as bone. Accordingly, measurements of changes in the length of ligaments under various dynamic conditions are useful indicators of soft-tissue loading. Current stereo-optic methods of measuring changes in ligament length provide three-dimensional measurements of tissue strains without the need for direct ligamentous contact. In many applications in research and industry, it is necessary to measure the deformation of mechanical structures during application of loads. Typically, this is achieved through the attachment of transducers to the loaded object. These transducers convert small changes in length between points of attachment to the underlying object to an electrical signal which can be recorded and converted to surface displacements. Another method is non-contacting and uses optical methods to record the relative position of markings drawn on the surface of deforming objects, or unique surface features. By tracking the spatial location of these markings, before and after loading, it is possible to determine the displacement that has occurred. While these methods are satisfactory for many applications, they have the following inherent limitations:
a) Excessive bulk for use in situations where space is limited;
b) Excessive weight for use with fragile or flexible substrates;
c) Expensive, especially optical systems;
d) Difficulties with reliable attachment to substrate surfaces;
e) Poor accuracy and/or repeatability;
f) Unacceptable noise and/or signal drift.
These weaknesses are particularly apparent in the testing of low-modulus and viscoelastic materials, especially biological tissues. In this application, coupling to tissues is often unreliable and leads to measurement artifacts. The present invention addresses each of the deficiencies listed with a sensor which is extremely light-weight, compact, accurate and repeatable. This invention can be used in any application where measurement of movement is desired.